Multifrequency Laser Emission Research Articles

Continuous-Wave Multifrequency Laser Emission Generated Through Stimulated Raman Scattering and Four-Wave Raman Mixing in an Optical Cavity

The frequency of a continuous-wave laser was converted via high-order stimulated Raman scattering and four-wave Raman mixing in a high-finesse optical cavity. The threshold for the generation of a Stokes beam was determined by the Raman gain coefficient and the loss in the cavity. The intracavity power of the second-order Stokes beam increased with an increase in pump power, whereas the power of the first-order Stokes beam stayed constant. The output power of the anti-Stokes beam was low when there was a phase mismatch between the pump and the first-order Stokes beam. The anti-Stokes beam, however, was enhanced by decreasing the pressure of the Raman active medium. This suggests that the dispersion can be used to improve the efficiency of the intracavity four-wave Raman mixing.

Thermal loss mechanism in the generation of multifrequency laser emission via stimulated Raman scattering and four-wave Raman mixing studied by photothermal refraction spectroscopy

The heat produced in conjunction with the processes of stimulated Raman scattering and four-wave Raman mixing in hydrogen was measured by photothermal refraction spectroscopy. Many vibrational, rotational, and vibrationally shifted rotational Raman lines are exclusively/simultaneously generated by changing the polarization of the laser beam and the hydrogen pressure. Thermal loss occurs predominantly from vibrational Raman scattering, which can be ascribed to a large Raman shift frequency of 4155 cm-1 for the vibrational transition. In contrast to stimulated Raman scattering, little or no thermal loss is observable during the process of four-wave Raman mixing.

The Generation of Powerful Rainbow-Color Laser Emission by Four-Wave Raman Mixing for Display and Illumination.

In order to generate a multifrequency laser emission, consisting of the entire rainbow of colors, two approaches are demonstrated and compared for commercial application, such as displays and illumination. One approach uses a second harmonic emission of a Nd:YAG laser emitting at 532 nm as the main pump beam and a dye laser, which is pumped by a part of the Nd:YAG laser, as a seed beam. These beams are coaxially aligned and are focused into two Raman cells filled with hydrogen to generate multifrequency laser emission based on four-wave Raman mixing. The other approach is more straightforward and involves an elliptically polarized second harmonic emission of a Nd:YAG laser, instead of a two-color laser beam, which is simply focused into the Raman cells. The entire rainbow colors (more than 20 emission lines from 400 nm to 800 nm) are generated in both the approaches. More efficient generation of the regular (quasi-equally spaced) spectral lines with a flatter intensity distribution is achieved by the former approach. The output power obtained is 600 mW (60 mJ×10 Hz).

Generation of high-order rotational lines by four-wave Raman mixing using a high-power picosecond Ti:Sapphire laser

More than thirty rotational lines equally spaced by 587 cm−1 are generated simultaneously in the vicinity of the fundamental line by four-wave Raman mixing using a high-power picosecond Ti:Sapphire laser as a pump source and hydrogen as a Raman medium. Since the wavelength of this multifrequency laser emission extends from the near-infrared to the near-ultraviolet, it can be utilized as a tunable light source for picosecond spectroscopy. Because of the wide spectral bandwidth available, this procedure has great potential for the generation of ultrashort laser pulses by mode-locking these emission lines.

Generation of multifrequency laser emission quasi equally spaced throughout the entire visible region

A circularly polarized, monochromatic laser beam is focused into a Raman cell, which contains hydrogen to generate rotational stimulated Raman emission. After linear polarization, this two-color (separated by 587 cm(-1)) laser beam is focused several times into a second Raman cell that is filled with hydrogen to generate a multifrequency laser emission. Many rotational and vibrational lines are generated efficiently by this multipass effect. Eighteen colors that are quasi equally spaced with a rather flat intensity distribution are generated throughout the entire visible region. The present multifrequency laser emission may be advantageously used for illumination in a higher-grade display, such as a laser light show.

Effect of laser linewidths on efficiency in generation of equally-spaced multifrequency beam by four-wave rotational Raman mixing

A two-color dye laser system whose linewidths can be changed independently is constructed for an investigation of the efficiency in generation of equally-spaced multifrequency laser emission by the two-color stimulated Raman effect. The efficiency in generation of a vibrational line is reduced substantially by increasing the linewidth of the laser, while it is not reduced drastically for rotational lines. Consequently, the rotational lines are more pronounced by broadening the laser linewidth. These results are explained by a difference in the processes for generation of these emissions, i.e. conventional Raman scattering for vibrational emission and four-wave Raman mixing for rotational emission. The present investigation implies that equally-spaced multifrequency laser emission can be generated efficiently in a wide spectral domain using a transform-limited femtosecond (high peak power and broad linewidth) laser pulse, which is required for generation of an ultrashort optical pulse in the scheme proposed in Optics Comm. 96 (1993) 94.

Multifrequency laser emission generated by two-color stimulated Raman effect using a single-frequency laser beam and a dye-Raman composite resonator

A single-color circularly polarized laser beam is focused into pressurized hydrogen to generate rotational stimulated Raman emission. After being corrected to a linearly polarized beam, this two-color laser beam is passed through a dye amplifier and is focused into pressurized hydrogen, again to generate multifrequency laser emission by the two-color stimulated Raman effect. The laser beam is further confined in a resonator, which enhances intracavity intensity leading to increased efficiency. In these experiments, more than 11 rotational lines are generated simultaneously at 5 atm, and many additional vibrationally shifted rotational lines are generated at 9 atm.

Generation of multifrequency laser emission and its application as an excitation source in supersonic jet spectrometry

Generation of multifrequency laser emission and its application as an excitation source in supersonic jet spectrometry

Generation of multi-frequency laser emission using an active frequency shifted feedback cavity

A dye laser possessing frequency shifted feedback is employed to create a wide spectrum of discrete, narrowly spaced frequency components. A monochromatic signal injected at a particular frequency, is shifted up by a fixed frequency interval on each round trip using an intra-cavity acousto-optic modulator (AOM). The gain in the laser compensates for the loss and permits the signal to circulate in the resonator several hundred times, leading to spectra extending over tens of gigahertz. In the present case, the AOM frequency, and thus the frequency spacing of the components, is 80 MHz. Moreover, since the light is shifted away from the frequency of injection, it is possible to create spectra with extremely sharp edges but otherwise essentially broadband. Calculations using a rate equation model are in semi-quantitative agreement with the observed results.